This invention relates generally to the field of data handling systems, and more particularly, but not by way of limitation, to an apparatus and method for adjusting bearing preload in an actuator pivot system to produce a population of nominally identical data handling systems, such as disc drives, having actuators with substantially uniform mechanical frequency response characteristics.
Disc drives are data handling systems used to perform primary data storage operations in modem computer systems and networks. A typical disc drive comprises a head-disc assembly (HDA) which houses mechanical portions of the drive, and a printed circuit board assembly (PCBA) mounted to an outer surface of the HDA which supports electronic circuitry used to control the HDA.
Typically, an HDA comprises a number of magnetic discs affixed to, and rotated by, a spindle motor at a constant high speed. An actuator supports an array of read/write heads adjacent the disc surfaces. The surface of each disc is a data recording surface divided into a series of generally concentric recording tracks radially spaced across a band having an inner diameter and an outer diameter. The data tracks extend around the surfaces of the discs and data are stored to the tracks by the heads in the form of magnetic flux transitions. Typically, each data track is divided into a number of data sectors that store fixed sized data blocks.
An actuator motor, such as a voice coil motor (VCM), rotates the actuator, and hence the heads, across the disc surfaces. The control circuitry on the PCBA includes a read/write channel which interfaces with the heads to transfer data between the tracks and a host computer, and a servo control system which drives the VCM to provide head positional control, based on servo data stored in servo fields interspersed among the data sectors and written during disc drive manufacturing.
Continued demand for disc drives with ever increasing levels of data storage capacity and data throughput have led disc drive manufacturers to seek ways to increase the storage capacity of each disc surface and improve drive operating efficiencies. At the same time, disc drive manufacturers are under continual pressure to reduce the cost per megabyte associated with the manufacture and marketing of their product offerings.
One area for opportunity is the actuator used within the disc drive. The industry has substantially settled on a design featuring a flat coil rotary actuator with a body portion rotatable about a bearing assembly and actuator arms which project from the body portion toward the discs. This portion of the actuator is sometimes referred to as an xe2x80x9cE-blockxe2x80x9d or xe2x80x9cactuator core.xe2x80x9d The E-block rotates using a pivot system typically comprising a cartridge bearing assembly having an inner shaft, an outer cylindrical sleeve and a pair of axially displaced bearing assemblies fixed therebetween. Generally, the outer surface of the outer sleeve is attached in the central bore in the E-block. Tolerance rings are also sometimes used to aid the assembly of these components.
While operable, there are nevertheless limitations associated with this approach. The bore wall of the E-block, which necessarily requires a uniform diameter to accommodate the cartridge bearing assembly, can be subject to elastic deformation (buckling) under high force access operations such as during seeks when the E-block is rapidly accelerated and decelerated to move a head from one track to another. Such buckling is most pronounced along a plane that intersects the actuator coil and operates to move the coil sway mode to a lower frequency, negatively affecting servo performance.
Another limitation is that, for a given bore size, the cartridge bearing assembly artificially limits the maximum bearing size by the wall thicknesses of the inner and outer sleeves. With decreasing size, these wall thicknesses have become a significant portion of the overal size of the pivot system. Moreover, the use of the bearing cartridge assembly increases material costs of the drives and introduces part tolerance variations that can affect the frequency response of the system.
It is desirable when producing a large population of disc drives to provide the drives with substantially identical mechanical characteristics. Unfortunately, these and other factors have been found to contribute to large variations in the locations of the natural frequencies of the actuators. Hence, different drives can have substantially different mechanical response characteristics which can adversely affect servo performance during operation.
Accordingly, there is a need for an improved, cost-effective approach to assembling and configuring actuator pivot systems to provide a population of data handling systems with substantially identical mechanical response characteristics, and it is to such improvements that the present invention is directed.
The present invention is directed to an apparatus and method for providing an actuator of a data handling system, such as a disc drive, with desired mechanical response characteristics.
In accordance with preferred embodiments, a disc drive is provided with a rotary actuator which supports a read/write head adjacent a recording surface of a rotatable disc. The actuator rotates about a pivot system comprising a stationary shaft and a bearing assembly comprising a stationary inner race coupled to the shaft and a rotatable outer race coupled to the actuator.
A fastener, such as a threaded screw, is provided to engage the shaft and apply a selected amount of axially directed force on the inner race to provide the actuator with the desired mechanical response characteristics. The fastener preferably extends through a top cover of the disc drive and presses a contact area of the top cover onto the inner race.
In a related aspect, the pivot system further comprises a second bearing assembly axially displaced from the first bearing assembly, the second bearing assembly comprising a stationary inner race coupled to the shaft and a rotatable outer race coupled to the actuator. The actuator includes a central bore through which the shaft extends, and a circumferentially extending step radially extends within the bore in a direction toward the shaft and abuttingly engages the respective outer races of the first and second bearing assemblies. The step reduces buckling of the actuator during high energy access operations.
In another related aspect, a compressive member circumferentially extends about the shaft and applies an axially directed force against the respective inner races of the first and second bearing assemblies to counteract the force applied by the fastener and increase the resolution of the fastener.
The desired mechanical resonance characteristics are preferably selected by steps of applying a broad spectrum excitation to the actuator, such as by the application of swept sine currents to an actuator motor; measuring mechanical response characteristics of the actuator in response to the broad spectrum excitation; and repetitively adjusting the fastener to increase the amount of axially directed force until the measured mechanical response characteristics of the actuator reach a desired level. Preferably, these steps are carried out during the writing of servo position data during disc drive manufacturing using a servo track writer (STW) station, and serve to produce a population of nominally identical disc drives with closely controlled and matched response characteristics.
These and various other features and advantages which characterize the present invention will be apparent from a reading of the following detailed description and a review of the associated drawings.